This invention relates generally to apparatus for controlling fuel supply to internal combustion engines, and more particularly to such apparatus which is capable of correcting the amount of fuel injected into engine cylinders on acceleration.
The amount of fuel to be injected into engine cylinders on acceleration is required to be larger than that on normal operation of the engine. In conventional fuel supply apparatus for internal combustion engines, therefore, the difference between necessary amount of fuel and normal amount of fuel is calculated as an additional amount of fuel to be injected so that actual amount of fuel to be injected equals the necessary amount of fuel. However, there is a time lag in fuel supply due to various factors, such as a time duration between the detection of engine parameters and computation of the amount of fuel to be injected by way of a control unit, a time duration between an instant of command of fuel increase and an instant of actual fuel injection. For instance, in the case of a system of simultaneous injection to all the cylinders once per revolutions, there is a cylinder to which fuel is injected after intake stroke, and therefore there occurs delay in fuel supply till a subsequent intake stroke. Owing to such time lag the amount of fuel to be injected cannot accurately follow the variation in the amount of intake air resulting in excessively lean air/fuel ratio which leads to a phenomenon such as backfire.
One approach for resolving the above problem is disclosed in Japanese patent provisional publication No. 56-148633. According to the technique disclosed in the above publication, a fuel correction apparatus for EFI engine is provided where the apparatus comprises a unit for determining basic fuel injection time duration on the basis of at least two engine parameters among engine speed, throttle valve opening degree, intake vacuum and so on, a unit for injecting fuel under given pressure by opening nozzles for the above basic fuel injection time duration, a unit for obtaining increasing rate of the throttle valve opening degree, and a unit for additionally injecting fuel by temporarily opening the nozzles for a given period of time when the above-mentioned increasing rate exceeds a first setting value. In other words, when the opening speed of the the throttle valve is above a setting value, an additional fuel injection which is different from normal fuel injection synchronized with engine rotation is effected so as to correct the amount of fuel injected into engine cylinders.
However, the above-mentioned setting value is constant, and cannot be changed depending on the engine operating condition. Therefore, when the operating condition suddenly varies, such that the opening speed of the throttle valve varies, it is necessary to inject the above-mentioned additional fuel with the throttle valve opening degree being detected at an interval of a short period of time of 10 to 20 ms. Furthermore, when the opening speed is around a critical value, above which additional fuel supply is effected, additional fuel injection is performed many times (such as 6 to 8 times) resulting in excessively rich air/fuel mixture. As a result, there occurs a problem of the increase in noxious components in the exhaust gases.